1. Field of the invention
The present invention relates to a still camera system, more particularly to a still camera system which is designed to permit selectively mounting a still video back having a solid image pickup element for picking up still images and a back for film onto a camera body.
2. Description of the Prior Art
Electronic still cameras for recording on a magnetic recording disk the still images picked up with a solid image pickup element such as CCD (charge coupled device) are known, as introduced for example in "Nikkei Electronics", pages 80 to 85, issued on July 2, 1984 in Japan. The present applicant also previously filed an application on a still camera of a system to mount a still video back selectively onto a camera body, as Japanese Utility Model Application No. 36821/1986. According to said system, a still video back containing a solid image pickup element and an image processing circuit, etc. is interchangeably mountable onto a camera body carrying an ordinary back for film, and when it is mounted on the camera body, the whole unit is compact to provide an image resembling that of the commercially available still cameras. When a back for film is mounted in place of the still video back, the camera is usable as an ordinary still camera to give exposures on a film.
By the way, in an ordinary camera using a 35 mm roll film, in actuating an electronic flash unit there is in practice to adjust the amount of the flash light of the flash unit.
In FIG. 1 there is shown an example of a camera and an electronic flash unit to which such prior art is applied. In FIG. 1, the part 1 shows a camera body, and the part 2 an electronic flash unit. The camera body 1 is furnished with a photoelectric conversion element (D.sub.1) arranged to be sensitive to the light reflected by the film 3 out of the light incident on the camera inside through the interchangeable taking lens; a conversion circuit 5 for logarithmically compressing the output current of the photoelectric conversiion element (D.sub.1) into a voltage by a diode (D.sub.2) and an operation amplifier 4; an adder 6 for adding the film speed voltage (Sv) set in proportion to the film speed to the aforementioned voltage after conversion; a transistor (Q.sub.1) for logarithmically extending said output voltage; a capacitor (C.sub.1) for integrating the logarithmically extended current; a switch (S.sub.1) for controlling the integrating action of said capacitor (C.sub.1); and a comparator 7 for comparing the charge voltage of said capacitor (C.sub.1) with the predetermined proper exposure level (V.sub.1). Further, the camera body 1 is furnished with an X contact (Sx) which is put ON when, for example, the running of the first curtain of the focal plane shutter has been completed to make the shutter fully open; a first terminal (T.sub.1) for giving the flash start signal (ST.sub.1) produced by switching ON the X contact (Sx) to the electronic flash unit 2; an inverter 8 for inverting the signal (ST.sub.2) given from the electronic flash unit 2 through the second terminal (T.sub.2) to give it to the control terminal (T.sub.7) of the switch (S.sub.1); and a third terminal (T.sub.3) for transmitting a flash stopping signal (ST.sub.3) produced from the comparator 7 to the side of the electronic flash unit 2. On the other hand, the electronic flash unit 2 has a flashing section 9 including a xenon tube 10; a flash stopping section (S.sub.2) to be put O by the aforesaid flash stopping signal (ST.sub.3); a flash starting section (S.sub.3); a comparator 11 for comparing the charged voltage of the main capacitor in the flashing section 9 with the predetermined fixed voltage (V.sub.2); an inverter 13 for inverting the low level signal produced by switching ON the main switch (S.sub.4) for the electronic flash unit to the high level signal and applying to the second input (I.sub.2) of an AND gate 12; a timer circuit 14 for outputting a low level signal for a certain duration under the aforesaid flash starting signal; an inverter 15 for converting the low level flash starting signal into the high level and giving it to the flash starting section (S.sub.3); and the 4th, 5th, and 6th terminals (T.sub.4), (T.sub.5), and (T.sub.6) corresponding to the first, second, and third terminals (T.sub.1), (T.sub.2), and (T.sub.3). To the first input (I.sub.1) of the aforesaid AND gate 12 the output of the aforesaid comparator 11 is exerted, and to the third input (I.sub.3) the output of the timer circuit 14 is exerted, respectively.
Then, to explain the operation, when the electronic flash main switch (S.sub.4) is put ON, the point (a) comes to have an earth potential. However, as the inverter 13 converts it into a high level, the second input (I.sub.2) of the AND gate 12 assumes a high level. Also, the third input (I.sub.3) of the AND gate 12 is on a high level, because the flash starting signal (ST.sub.1) has not reached the fourth terminal (T.sub.4). When, under such a condition, charging to the main capacitor in the electronic flash unit is completed and a high level signal is given to the first input (I.sub.1) of the AND gate 12 from the comparator 11, a high level signal is outputted from the AND gate 12, and the said output is inverted to a low level by the inverter 8 in the camera body 1. As a result, the switch (S.sub.1) assumes a state of being turned ON to short-circuit the capacitor (C.sub.1).
Then, when the shutter release button is pressed and, simultaneously with full opening of the shutter, the X contact (Sx) is put on to generate the low level flash starting signal (ST.sub.1), a low level signal is generated from the timer circuit to turn the output of the AND gate 12 to a low level. Accordingly, a high level signal is applied to the control terminal (T.sub.7) of the switch (S.sub.1) through the inverter 8 to make the swtich (S.sub.1) OFF state. On the other hand, in the electronic flash unit 2, the flash starting signal (ST.sub.1) is converted by the inverter 15 into a high level and applied to the flash starting section (S.sub.3). As a result, the flash starting section (S.sub.3) is switched ON to have the flashing section 9 flash. With the flashing of the electronic flash unit, the light reflected from the object comes into the camera body through the interchangeable lens (taking lens), and a part of it is reflected by the film 3 to reach the photoelectric conversion element (D.sub.1). The photoelectric conversion element (D.sub.1 ) outputs the current proportionate to the intensity of light on the film face. This output current is modified into a logarithmically compressed voltage by the conversion circuit 5, followed by combination with the film speed voltage (Sv) by the adder 6 and added to the base of the transistor (Q.sub.1). The output current generated on the collector side of the transistor (Q.sub.1) charges the capacitor (C.sub.1). The charge voltage of this capacitor (C.sub.1) corresponds to the exposure level. When the capacitor (C.sub.1) goes on being charged and its charge voltage reaches the proper exposure level (V.sub.1), the output of the comparator 7 comes to a high level. This high level acts as a flash stopping signal (ST.sub.3) on the flash stopping section (S.sub.2) to stop flashing of the xenon tube 10. In the manner as described, on attainment of the proper exposure level, flashing of the electronic flash unit is stopped to complete the light adjusting operation of the electronic flash unit.
However, when the condition is such that, instead of the back for film, a still video back is mounted on the camera body, because of the lack of the reflecting object on the position corresponding to the film surface, flash level adjusting operation of the electronic flash unit is not feasible with the conventional construction as above.